Peter Brukner

Risk Factors for Stress Fractures in Track and Field Athletes A Twelve-Month Prospective Study

The aim of this 12-month prospective study was to investigate risk factors for stress fractures in a cohort of 53 female and 58 male track and field athletes, aged 17 to 26 years. Total bone mineral content, regional bone density, and soft tissue composition were meas ured using dual-energy x-ray absorptiometry and an thropometric techniques. Menstrual characteristics, current dietary intake, and training were assessed us ing questionnaires. A clinical biomechanical assess ment was performed by a physical therapist. The inci dence of stress fractures during the study was 21.1%, with most injuries located in the tibia. Of the risk factors evaluated, none was able to predict the occurrence of stress fractures in men. However, in female athletes, significant risk factors included lower bone density, a history of menstrual disturbance, less lean mass in the lower limb, a discrepancy in leg length, and a lower fat diet. Multiple logistic regression revealed that age of menarche and calf girth were the best independent predictors of stress fractures in women. This bivariate model correctly assigned 80% of the female athletes into their respective stress fracture or nonstress frac ture groups. These results suggest that it may be pos sible to identify female athletes most at risk for this overuse bone injury.

The Incidence and Distribution of Stress Fractures in Competitive Track and Field Athletes A Twelve-Month Prospective Study

The incidence and distribution of stress fractures were evaluated prospectively over 12 months in 53 female and 58 male competitive track and field athletes (age range, 17 to 26 years). Twenty athletes sustained 26 stress fractures for an overall incidence rate of 21.1%. The incidence was 0.70 for the number of stress frac tures per 1000 hours of training. No differences were observed between male and female rates (P > 0.05). Twenty-six stress fractures composed 20% of the 130 musculoskeletal injuries sustained during the study. Although there was no difference in stress fracture incidence among athletes competing in different events (P > 0.05), sprints, hurdles, and jumps were associated with a significantly greater number of foot fractures; middle- and long-distance running were as sociated with a greater number of long bone and pelvic fractures (P < 0.05). Overall, the most common sites of bone injuries were the tibia with 12 injuries (46%), followed by the navicular with 4 injuries (15%), and the fibula with 3 injuries (12%). The high incidence of stress fractures in our study suggests that risk factors in track and field athletes should be identified.

Risk Factors for Stress Fractures

Preventing stress fractures requires knowledge of the risk factors that predispose to this injury. The aetiology of stress fractures is multifactorial, but methodological limitations and expediency often lead to research study designs that evaluate individual risk factors. Intrinsic risk factors include mechanical factors such as bone density, skeletal alignment and body size and composition, physiological factors such as bone turnover rate, flexibility, and muscular strength and endurance, as well as hormonal and nutritional factors. Extrinsic risk factors include mechanical factors such as surface, footwear and external loading as well as physical training parameters. Psychological traits may also play a role in increasing stress fracture risk. Equally important to these types of analyses of individual risk factors is the integration of information to produce a composite picture of risk.The purpose of this paper is to critically appraise the existing literature by evaluating study design and quality, in order to provide a current synopsis of the known scientific information related to stress fracture risk factors. The literature is not fully complete with well conducted studies on this topic, but a great deal of information has accumulated over the past 20 years. Although stress fractures result from repeated loading, the exact contribution of training factors (volume, intensity, surface) has not been clearly established. From what we do know, menstrual disturbances, caloric restriction, lower bone density, muscle weakness and leg length differences are risk factors for stress fracture.Other time-honoured risk factors such as lower extremity alignment have not been shown to be causative even though anecdotal evidence indicates they are likely to play an important role in stress fracture pathogenesis.

Epidemiology and site specificity of stress fractures

Clinically, stress fractures appear to be a common overuse injury among athletes and in military recruits undertaking basic training; however, there is a lack of sound epidemiologic studies describing stress fracture occurrence in athletes. Few have directly compared stress fracture rates between sports to establish which poses the greatest risk for this injury. Furthermore, incidence rates, expressed in terms of exposure, have rarely been reported for stress fractures in athletes. Nevertheless, available data suggest that runners and ballet dancers are at relatively high risk for stress fractures. Although a gender difference in rates is clearly evident in military populations, this is less apparent in athletes. Other participant characteristics, such as age and race, may also influence stress fracture risk. The most common site of stress fracture in athletes is the tibia, although the site reflects the nature of the load applied to the skeleton. Stress fracture morbidity, expressed as the time until return to sport or activity, varies depending on the site. Generally, a period of 6 to 8 weeks is needed for healing; however, stress fractures at certain sites, such as the navicular and anterior tibial cortex, are often associated with protracted recovery and, in some cases, termination of sporting pursuits.

Stress fractures: A review of 180 cases

OBJECTIVE To review the cases of stress fracture seen over a 2-year period at a sports medicine clinic. DESIGN One hundred and eighty cases diagnosed as stress fractures on the basis of clinical picture and radiological evidence were reviewed. The following features of each stress fracture were noted: age, sex, site, sport/activity. SETTING A sports medicine centre in Melbourne, Australia. PATIENTS The average age was 21.8 years. Seventy eight of these stress fractures were seen in women, 102 in men. RESULTS The most common sites of stress fractures were the metatarsal bones (n = 42), tibia (n = 36), fibula (n = 30), tarsal navicular (n = 26) and pars interarticularis (n = 17). The most common sport was track (n = 54). Other common sports activities were jogging/distance running (n = 35), dance (n = 32) and Australian football (n = 14). The distribution of sites of stress fractures varied from sport to sport. Among the track athletes (n = 54), navicular (n = 19), tibia (n = 14) and metatarsal (n = 9) were the most common stress fracture sites. The distance runners (n = 35) predominantly sustained tibia (n = 15), and fibula (n = 8) stress fractures, while metatarsal stress fractures (n = 18) were the most common among dancers. The distribution of sports varied with the site of the stress fracture. In the metatarsal stress fractures (n = 42), dance was the most common activity. Distance running (n = 15) and track (n = 14) were the most common sports in the group to have sustained tibia stress fractures (n = 36). Track athletes (n = 14) were particularly prevalent in the navicular stress fracture group (n = 26). CONCLUSION The distribution of sites of stress fractures in this study shows some differences from previously published studies.

Natural History of Concussion in Sport Markers of Severity and Implications for Management

Background Evidence-based clinical data are required for safe return to play after concussion in sport. Purpose The objective of this study was to describe the natural history of concussion in sport and identify clinical features associated with more severe concussive injury, using return-to-sport decisions as a surrogate measure of injury severity. Study Design Cohort study (prognosis); Level of evidence, 3. Methods Male elite senior, elite junior, and community-based Australian Rules football players had preseason baseline cognitive testing (Digit Symbol Substitution Test, Trail-Making Test—Part B, and CogSport computerized test battery). Players were recruited into the study after a concussive injury sustained while playing football. Concussed players were tested serially until all clinical features of their injury had resolved. Results Of 1015 players, 88 concussions were observed in 78 players. Concussion-associated symptoms lasted an average of 48.6 hours (95% confidence interval, 39.5-57.7 hours) with delayed return to sport correlated with ≥4 symptoms, headache lasting ≥60 hours, or self-reported “fatigue/fogginess.” Cognitive deficits using the Digit Symbol Substitution Test and Trail-Making Test—part B recovered concomitantly with symptoms, but computerized test results recovered 2 to 3 days later and remained impaired in 35% of concussed players after symptom resolution. Conclusion Delayed return to sport was associated with initially greater symptom load, prolonged headache, or subjective concentration deficits. Cognitive testing recovery varied, taking 2 to 3 days longer for computerized tests, suggesting greater sensitivity to impairment. Therefore, symptom assessment alone may be predictive of but may underestimate time to complete recovery, which may be better estimated with computerized cognitive testing.

Bone mass and bone turnover in power athletes, endurance athletes, and controls: A 12-month longitudinal study

Strain magnitude may be more important than the number of loading cycles in controlling bone adaptation to loading. To test this hypothesis, we performed a 12 month longitudinal cohort study comparing bone mass and bone turnover in elite and subelite track and field athletes and less active controls. The cohort comprised 50 power athletes (sprinters, jumpers, hurdlers, multievent athletes; 23 women, 27 men), 61 endurance athletes (middle-distance runners, distance runners; 30 women, 31 men), and 55 nonathlete controls (28 women, 27 men) aged 17-26 years. Total bone mineral content (BMC), regional bone mineral density (BMD), and soft tissue composition were measured by dual-energy X-ray absorptiometry. Bone turnover was assessed by serum osteocalcin (human immunoradiometric assay) indicative of bone formation, and urinary pyridinium crosslinks (high-performance liquid chromatography) indicative of bone resorption. Questionnaires quantified menstrual, dietary and physical activity characteristics. Baseline results showed that power athletes had higher regional BMD at lower limb, lumbar spine, and upper limb sites compared with controls (p < 0.05). Endurance athletes had higher BMD than controls in lower limb sites only (p < 0.05). Maximal differences in BMD between athletes and controls were noted at sites loaded by exercise. Male and female power athletes had greater bone density at the lumbar spine than endurance athletes. Over the 12 months, both athletes and controls showed modest but significant increases in total body BMC and femur BMD (p < 0.001). Changes in bone density were independent of exercise status except at the lumbar spine. At this site, power athletes gained significantly more bone density than the other groups. Levels of bone formation were not elevated in athletes and levels of bone turnover were not predictive of subsequent changes in bone mass. Our results provide further support for the concept that bone response to mechanical loading depends upon the bone site and the mode of exercise.

Ice-water immersion and delayed-onset muscle soreness: a randomised controlled trial

Objective: To determine if ice-water immersion after eccentric quadriceps exercise minimises the symptoms of delayed-onset muscle soreness (DOMS). Design: A prospective randomised double-blind controlled trial was undertaken. 40 untrained volunteers performed an eccentric loading protocol with their non-dominant leg. Interventions: Participants were randomised to three 1-min immersions in either ice water (5±1°C) or tepid water (24°C). Main outcome measures: Pain and tenderness (visual analogue scale), swelling (thigh circumference), function (one-legged hop for distance), maximal isometric strength and serum creatine kinase (CK) recorded at baseline, 24, 48 and 72 h after exercise. Changes in outcome measures over time were compared to determine the effect of group allocation using independent t tests or Mann–Whitney U tests. Results: No significant differences were observed between groups with regard to changes in most pain parameters, tenderness, isometric strength, swelling, hop-for-distance or serum CK over time. There was a significant difference in pain on sit-to-stand at 24 h, with the intervention group demonstrating a greater increase in pain than the control group (median change 8.0 vs 2.0 mm, respectively, p = 0.009). Conclusions: The protocol of ice-water immersion used in this study was ineffectual in minimising markers of DOMS in untrained individuals. This study challenges the wide use of this intervention as a recovery strategy by athletes.

Risk factors for stress fractures in female track-and-field athletes: a retrospective analysis.

The incidence and nature of stress fractures and the relationship of potential risk factors to stress-fracture history were investigated retrospectively in a group of 53 female competitive track-and-field athletes. Forty-five stress fractures, diagnosed by clinical findings and bone scan, radiograph, or CT scan, were reported in 22 women. Tibial fractures were the most common (33%). There was no significant difference in bone mineral density at the lumbar spine and tibia/fibula or in percentage body fat and total lean mass when comparing the groups with and without a stress-fracture history. Athletes with a past stress fracture were significantly older at menarche and were more likely to have experienced a history of menstrual disturbance (p < 0.05). Analysis of dietary behavior found that athletes with stress fractures scored significantly higher on the EAT-40 test and were more likely to engage in restrictive eating patterns and dieting. Multiple logistic regression showed that athletes with a history of oligomenorrhea were six times more likely to have sustained a stress fracture in the past, while those who were careful about their weight were eight times more likely. Prevention and treatment of stress fractures in female athletes should include a thorough assessment of menstrual characteristics and dietary patterns.

Magnetic Resonance Imaging Parameters for Assessing Risk of Recurrent Hamstring Injuries in Elite Athletes

Background Magnetic resonance (MR) imaging has established its usefulness in diagnosing hamstring muscle strain and identifying features correlating with the duration of rehabilitation in athletes; however, data are currently lacking that may predict which imaging parameters may be predictive of a repeat strain. Purpose This study was conducted to identify whether any MR imaging-identifiable parameters are predictive of athletes at risk of sustaining a recurrent hamstring strain in the same playing season. Study Design Cohort study; Level of evidence, 3. Methods Forty-one players of the Australian Football League who sustained a hamstring injury underwent MR examination within 3 days of injury between February and August 2002. The imaging parameters measured were the length of injury, cross-sectional area, the specific muscle involved, and the location of the injury within the muscle-tendon unit. Players who suffered a repeat injury during the same season were reimaged, and baseline and repeat injury measurements were compared. Comparison was also made between this group and those who sustained a single strain. Results Forty-one players sustained hamstring strains that were positive on MR imaging, with 31 injured once and 10 suffering a second injury. The mean length of hamstring muscle injury for the isolated group was 83.4 mm, compared with 98.7 mm for the reinjury group (P = .35). In the reinjury group, the second strain was also of greater length than the original (mean, 107.5 mm; P = .07). Ninety percent of players sustaining a repeat injury demonstrated an injury length greater than 60 mm, compared with only 58% in the single strain group (P = .01). Only 7% of players (1 of 14) with a strain <60 mm suffered a repeat injury. Of the 27 players sustaining a hamstring strain >60 mm, 33% (9 of 27) suffered a repeat injury. Of all the parameters assessed, only a history of anterior cruciate ligament sprain was a statistically significant predictor for suffering a second strain during the same season of competition. Conclusion A history of anterior cruciate ligament injury was the only statistically significant risk factor for a recurrent hamstring strain in our study. Of the imaging parameters, the MR length of a strain had the strongest correlation association with a repeat hamstring strain and therefore may assist in identifying which athletes are more likely to suffer further reinjury.